HORMONAL INDUCTION OF MELANOGENESIS IN HYPOPHYSECTOMIZED KILLIFISH (FUNDULUS HETEROCLITUS)1

Abstract

Experiments were done on hypophysectomized Fundulus hetero-clitus injected at 20[degree] C thrice weekly for one month. Alpha corticotropin had no effect on pigmentation at doses of 1 [mu]g or 10 [mu]g/g weight/ injection. Highly purified prolactin (35 I.U./mg), free from intermedin and ACTH, stimulated melanin synthesis in already developed melano-phores at doses of 1 [mu]g or 10 [mu]g/g weight/injection, but no new melano-phores were formed. Highly purified intermedin, ACTH-free, caused little or no increase in melanin synthesis but promoted the proliferation of new melanophores which spread over the belly. The threshold dose for this response was about 100 MSB units/g weight/injection; a maximal response was elicited by about 1000 MSH units. The response to a low dose of intermedin was potentiated by simultaneous administration of prolactin. Illumination promoted the proliferation of melanophores in response to combined treatment with intermedin + prolactin, but had no significant effect on the increased production of melanin. New melanophores differentiated from macrophage-like propigment cells already present in the dermis.